The act of constantly sharing the same opinion in a forum full of people who are obviously known to have the same opinion as yours,
therefor granting you free upvotes to said opinion, while gathering
downvotes to anyone that opposes you on the matter
Good examples:
The atheist section of Reddit
League of Legends' Boards
Any sort of
9Gag picture that goes against consoles/Frozen/Christianity
Nearly any website that governs itself through up and
downvotes, and inevitably estabilishes "approved" opinions, which leads to the formation of a circle jerk